Lionel Messi is used to being sought after by fans, celebrities and even fellow professionals but he was still caught by surprise when Jamaica's DeShorn Brown asked for a selfie following Argentina's 1-0 Copa America win.

Argentina won Group B with Saturday's victory, their second at the tournament in Chile, and were waiting yesterday to find out who they would face in the last eight after the final round of Group C matches.

Striker Brown, who had been substituted near the end of the match at Vina del Mar, picked up his mobile phone as soon as the final whistle went and ran onto the pitch to find Messi.

"I had thought about it before the match so that's why I took (the phone) to the bench. As soon as (the match) finished ... I took the picture," Brown said.

"Messi is the best in the world, a star, and that's a photo I'll have as a souvenir all my life."

Argentina's captain laughed as he recalled what had happened.

"He surprised me. On top of that I was annoyed about how the match had gone despite our win ... but when I saw the phone I realised what was going on. It's really nice when a colleague asks me for that," Messi said.

Argentina were all over Jamaica in the first half and should have had more than Gonzalo Higuain's early goal. They hit the bar twice before losing the initiative alarmingly in the final quarter of the match.

They managed to defend their lead and avoid what happened in their opening match when they gave away a two-goal lead to Paraguay who scored twice in the last half hour for a 2-2 draw.

"In the first half we created lots of chances, we found the spaces but couldn't score another goal," said Messi, who was making his 100th appearance for Argentina.

"It got tougher for us in the second half, the rhythm dropped and we played much more slowly, that's a fact... I don't know if it's a physical issue, I don't know why it happened to us."

Messi said Argentina would have to improve for the knockout phase if they want to win their first major title since the 1993 Copa America in Ecuador.

"That was our objective, to finish first (in the group) and think about what's to come. Another Copa starts now," he said.